"Evaporative loss control" or "evaporative emission control" are terms in general use to define a control, or method of controlling, hydrocarbons emissions to the atmosphere caused by evaporation of fuel. Included in this definition are those losses of evaporative nature from carburetor fuel bowl venting systems and from fuel tank venting systems.
When a hot engine is shut down, for instance, the residual heat in the engine can raise fuel bowl temperatures in some cases above 200.degree.F. It is not unusual that under certain climatic, and geographic conditions that the fuel bowl will boil completely dry, emitting the associated evaporated hydrocarbons to the atmosphere.
Fuel tank evaporative losses can occur in much the same manner although the associated temperatures involved are somewhat reduced. If a fuel tank is filled with relatively cool fuel from underground storage tanks and then left to stand under high ambient temperature conditions, an actual loss of liquid fuel can occurr, as well as evaporative loss. These losses occur through either vented fuel tanks or vented fuel filler caps; whichever are employed for the purpose of preventing fuel tank rupture and or pressure differentials which may affect fuel pump operation.
The losses so described have been estimated to be 10-15 percent of the total hydrocarbon discharge to the atmosphere associated with internal combustion engines. Some jurisdictions have legislated control of these losses.
There are in general two control systems being utilized by the industry. The first system is generally called a vapor-recovery system wherein the vapors are directed to the crankcase and utilizes a pressure vacuum relief fuel filler cap as a means of protecting the fuel tank from structural damage due to excessive pressurre differentials caused during severe operation or by system malfunction. The system is considered to be fail safe as the fuel filler cap design eliminates the possibility of damage to the system which may be hazardous.
The second system is generally called an adsorption-generation system, and is similar to the first system except that a charcoal canister is utilized to entrap vapors for later burning. This system also utilizes a pressure vacuum relief fuel filler cap.
In my prior U.S. Pat. Nos. 3,724,707 and 3,724,708 there are disclosed and claimed vacuum relief fuel filler caps suitable for use on vehicles equipped for "evaporative loss control" or "evaporative emission control."
Since that time, federal regulations have been enacted which call for increased integrity of the entire fuel system (of which the filler cap is part) after a vehicle has been subjected to a variety of crash and rollover tests. The filler caps described in U.S. Pat. Nos. 3,724,707 and 3,724,708 utilize a brass diaphragm or washer which temporarily deforms when the cap is applied to the filler neck to provide a sealed surface at the interface of the filler cap and filler neck. If this type of filler cap is impacted sharply, as could be expected during rear or side impact collisions, the brass diaphragm is usually deformed beyond its elastic limit; at which time the seal at the interface of the filler neck and filler cap is destroyed. This condition could allow the escape of liquid fuel and increase the possibility of fire following a crash exposing the occupants of a crashed vehicle to a second source of possible serious injury.
It is also desirable to provide means to prevent the cap from being applied with excessive force such that it is difficult to remove.
Among the objects of this invention are to provide a fuel filler cap which will allow for an increase in integrity of the fuel filler cap, at the interface with its associated filler neck, during vehicle crashes while retaining the features of "evaporative loss control" as described in the aforementioned patents; and to provide a fuel filler cap embodying a torque limiting feature.